Method of manufacturing stencils



Jan. 11, 1955 s. HOOVER I 2,699,113

METHOD OF MANUFACTURING STENCILS Filed Aug. 8, 1950 @j in; 2/

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United States Patent '0 METHOD OF MANUFACTURING STENCILS Keith S.Hoover, Elmhurst, 111., assignor to A. B. Dick Company, Niles, Ill., acorporation of Illinois Application August 8, 1950, Serial No. 178,220

9 Claims. (Cl. 101128.4)

This invention relates to stencils for use in ordinary duplicatingprocesses and it relates more particularly to an entirely new techniquefor the manufacture of stencils.

in the past, stencil openings through which ink may pass have beenformed in a stencil-base tissue by displacement of an impressionablecomposition that impregnates the stencil-base tissue and renders itimpervious to ink compositions. Displacement of the relatively softimpressionable composition hasbeen eifected by application of force, asby a stylus, compression die, or by impact with a typewriter key. Suchmeans for preparing stencils have restricted their use and hashandicapped. the adoption of stencil-duplicating processes in copy work,such as in ofiice copy work and the like.

It is an object of this inventionto provide a process for preparingstencils, a process which does notrely on the application of force inany form to produce the desired stencil openings.

Another object is to provide a process for preparing stencils whichpermits the advantageous use ,ofstencil duplicating processes for copywork.

A further object is to provide a new process for producing stencilsdirectly from an original copy whereby exact duplications thereof may bequickly and economically produced in large numbers.

A still further object is to provide a new method for producing stencilswhich makes use of heat developed by the materials in the original copyupon exposure to directed radiant energy for the purpose of developingcorresponding stencil openings through an ink barrier for the passage ofduplicating ink compositions in normal stencil duplicating processes,and it is a related object to produce a new and improved stencil of thetype described.

A still further object is to provide .a new technique for thepreparation of a stencil in a very rapid and expedient manner making useof low cost and readily available materials and which may be carried outwith simple and inexpensive equipment and which can be made available inpractically any location and operated without experienced labor.

A still further object is to produce a stencil and to provide a methodfor producing same of an unsupported film of ink impervious material.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, embodiments of the invention are shown in the accompanyingdrawing, in which Figure 1 is a schematic view partially in sectionillustrating the practice of this invention;

Figure 2 is an enlarged sectional elevational view showing thearrangement of parts in the practice of this invention;

Figure 3 is an enlarged top plan view of a stencil prepared by thetechnique illustrated in Figures 1 and 2, and

Figure 4 is a schematic view partially in section illustrating amodified manner of practicing this invention.

In accordance with this invention, a stencil having openingscorresponding to the'dark letter outlines of an original copy andthrough which ink may pass in normal duplicating processes to produce anumber of copies may be prepared by placing the original copy closelyadjacent or in surface contact with a film of plastic material havingthe characteristics of rearrangement on local heating to form openingsand then radiating the assembly. The radiant energy is substantiallyreflected or dissipated by'the light areas ofythe original,copyandsnbstantially absorbed by the materials forming the dark ,orprinted .areasof the 2,699,113 Patented Jan. 11, 1955 original copy andthereby converted into heat. The heat generated in such radiated areasshould be suflicient to cause thedesired rearrangement of the resinousmaterial in the corresponding areas of the plastic iilm to provideopenings through which ink may pass in normal stencil duplicating work.

Radiant energy capable of the. phenomenon of heat generation uponabsorption in the materials comprising the dark areas on the copy may bederived fromlight .sources rich in infrared, which includes rays havinga wave length ranging from 8,000 to 40,000 angstroms. These are abovethe visible range but below the extreme end of the infrared range.Radiant energy capable of the phenomenon of the type described may befound in the rays of the sun and therefore existsin ordinary daylightbut they may be developed in sufiiciently high concentration by anordinary flash bulb, or they may be generated by a tungsten filamentlight, carbon arc lamp, infra-red ray lamp, and the like. It has beenfound that the amount of heat developed depends chiefly upon theduration of exposure and the intensity of the usable radiant energy inthe light beams. The amount of heat developed also depends upon thedepth of the color in the copy and the character of the material ofwhich it is formed, which might be referred to as the"radiation-absorbingheat-producing material.

Microscopic examination of the'plastic film processed in the mannerdescribed and separated from the original onto which the radiant energywas directed, reveals a large number of openings arranged in arelatively uniform pattern throughout the area corresponding to the heatgenerating area of the copy. The openings are of sufficient dimension topermit stencil duplicating inks to pass in ordinary stencilingoperations. The resinous material which formerly occupied the openingsappears to have migrated and formed into globules or threads whichprovide a desirable lattice-work across the letter or stencil openingsthereby keeping the loop letters intact and imparting greater massintegrity to the unsupported film.

It seems as though movement of the resinous material into areas of thehigher concentration leaving openings therebetween may have resultedfrom the fact that the heated portion of the resinous 'film is reducedto fluid consistency and responsive to the surface forces operating inmasses of the type described, the resinous film breaking to provide openareas and areas of greater resin concentration.

Films of plastic material impervious to ink compositions and having thecharacteristics of the type described may be fabricated of plasticmaterials based upon resins such as polyvinylidene chloride (Saran) andcopolymers thereof with vinyl chloride or vinyl acetate, polystyrene,polyamides of the type formed by the reaction of a polybasic acid,preferably a dibasic acid, with a polyamine, preferably a diamine(Nylon), polytetrafluoroethylene (Teflon), polychlorotrifluoroethylene,polyethylene, rubber hydrochloride (Pliofilm), styrene-isobutylenecopolymer, styrene-acrylonitrile copolymer, and resinous films formed ofsuch fihn forming materials as polyvinyl chloride, vinyl chloride-vinylacetate copolymer, polyvinyl acetals, cellulose ethers and esters, suchas cellulose propipnate-butyrate, ethyl cellulose, nitro cellulose andthe It appears also that elastic memory of a stretched or oriented filmfosters the desirable rearrangement for separation of the resinousmaterial into open areas. and connecting threads of higher resinousconcentration. It has been found that an improved stencil can be formedat a lower temperature with a stretched or oriented unsupported filmthan with normal plastic film. By the use of .a stretched film, it ispossible to achieve a greater proportion of openings per unit area. Inmany instances, the use of a stretched or oriented plastic film is to bepreferred in the practice of this invention.

Orientation of the type described may be secured in films of the typeformed with polyvinylidene chloride, polystyrene,polytetrafluoroethylene, polyethylene, rubber hydrochloride,styrene-isobutylene copolymer, and styrene-acrylonitrile copolymer.

There is also reason to believe thatthe desired stencil openings in theplastic film may be .derived byway of a thermalactionsuch as bydecomposition or by chemical change in the resinous material of whichthe plastic film is formed. It has been found that this may be the caseespecially with resinous materials formulated with a halogen group, suchas in films formed of polyvinylidene chloride and copolymers thereofwith vinyl chloride or vinyl acetate, polyvinyl chloride, vinylchloride-vinyl acetate copolymers, chlorinated rubber, rubberhydrochloride, and the like, or by omission of stabilizer from theresinous material or by the addition of decomposition catalyst into thematerial of which the film is formed.

Film thicknesses in the range of 0.1 to 3.0 mils have been found mostsuitable but a plastic film having less thickness can be used if it isable to provide a barrier to the passage of ink. Greater filmthicknesses may also be used, especially if the heated plastic becomessubstantially fluid under processing conditions.

With the use of a photoflash lamp, it has been found possible to developtemperatures in excess of 400 F. in fractions of a second. With othersystems of the type described it is more difficult rapidly andeconomically to develop temperatures in excess of 350450 F. by thephenomenon of radiating the original copy. Limited only by the abilityto develop higher temperatures, the resinous material of which theplastic film is formed may be selected or else modified with softeners,plasticizers or the like to provide for a softening or liquefying pointwithin the temperature range of 150 to 450 F. It will be understood thatwhere the conditions for developing higher temperatures are achieved thesoftening range of suitable plastic material may be correspondinglybroadened.

Suitable plasticizers, softeners and the like for specific resinousmaterials or cellulosic materials may be selected by those skilled inthe art from the data available in the plastics and resinous fields. Forexample, polystyrene may be suitably plasticized with aryl phosphatessuch as tricresyl phosphate, chlorinated biphenyl, dibutyl phthalate,and the like. Usually an amount up to thirty-five percent by weightplasticizer is sufficient to impart the desired results, depending, ofcourse, upon the molecular weight of the polystyrene.

Polyvinyl chloride and vinyl chloride-vinyl acetate copolymers may beplasticized with dibutyl phthalate, diamyl phthalate, dioctyl phthalate,dibutyl cellosolve phthalate, tricresyl phosphate, and triglycol di-(2ethyl hexanoate) and vinyl chloride-vinyl acetate copolymer may also beplasticized with glycerol esters, camphor, triacetin and the like.Amounts up to forty percent by weight may be successfully used with theabove resins to impart the desired results.

Polyvinylidene chloride, which may be oriented while in theplastic-heated stage or while in a super-cooled stage, may beplasticized to the desired degree with any one of a number ofplasticizers or combinations thereof including polychloro derivatives ofaromatic hydrocarbons and ethers, such as polychloro biphenyl polychlorobenzene, and polychloro diphenyl oxide, dibenzyl ether, aralkyl ethers,tricresyl phosphate, hexachloroethylene, styrene oxide, phenoxypropylene oxide and the like.

Acrylic acid ester polymers, such as butyl methacrylate, ethyl acrylate,methyl methacrylate and the like may be plasticized in amounts rangingup to forty percent whenever necessary with dibutyl phthalate, dibutoxyethyl phthalate, chlorinated biphenyl, tricresyl phosphate, and thelike.

Suitable polyamides, preferably formulated of a dicarboxylic acid and adiamine, are usually sutficient in themselves when selected of apolymer, having a low molecular weight and a melting point below 400 F.,but the heat-sensitive point may be lowered by compounding withplasticizers such as the sulphonamides represented by p-toluenesulphonamide.

In the practice of this invention, illustrated schematically in Figurel, a plastic film of the type described is positioned on top of anoriginal copy 11 having the printed portion 12 uppermost and adjacentthe plastic film.

A photoflash lamp 13 is exploded over the assembly described and theradiant energy developed and directed onto the original copy (arrows) issubstantially reflected and dissipated by the light areas of the copyand absorbed by the material comprising the"radiation-absorbing-heatgenerating material of the copy (the darkerareas of the copy) and converted into heat. The heat developed is ofsuch proportion that rearrangement of the corresponding areas of theplastic film is occasioned. Numerous openings 14 are formed throughoutthe heated area leaving the resinous material therebetween in the formof connecting fibers or webs.

The plastic film separated from the copy has the characteristics of astencil from which a number of duplications of the original can be madeby normal stenciling operations.

As shown in Figure 4, the plastic film 20 may be placed on the undersideof the copy 21 with the printed portion 22 to be duplicated uppermost.By way of further modification, the assembly may be radiated bytraversing the copy with an energized tungsten filament 23 to directradiations 24 on to the printed side of the copy 21 whereby suchradiations are dissipated or substantially reflected by the light areasof the copy and absorbed and converted into heat by material in the darkareas of the copy. The heat is transmitted through the copy and to theplastic film where it functions to cause formation of the desiredstencil openings 25 through the corresponding areas of the plastic film.Upon separation, the plastic film may be used as a stencil in ordinarystencil duplicating processes.

Excellent results have been secured when the film 10 or 20 is compoundedof a polyvinylidene chloride resin which is oriented while in asupercooled state or in a heated plastic state. The polyvinylidenechloride may be used as a copolymer with vinyl chloride or vinylacetate, and the resin or the copolymer may be plasticized with up toforty percent by weight of a suitable plasticizer.

Instead of a polyvinylidene chloride, the film may be compounded of arubber hydrochloride, preferably oriented, having a softening point of205 to 250 F., or of styrene-isobutylene copolymer having a softeningpoint of about 200 to 300 F. In the event that the film is based on apolystyrene, it is preferred to make use of resin having a molecularweight between 35,000 and 65,000. When such or higher molecular weightpolymers are used the desired characteristics may be achieved withoutplasticizing the resinous materials but it may be plasticized with up tothirty percent by weight chlorinated biphenyl or tricresyl phosphate.Polyvinyl chloride having a softening point of about 200 to 300 F. maybe used with or without plasticizer. Vinyl chloride-vinyl acetatecopolymers having a melting point of between 200 to 300 F., with orwithout plasticizer, can also be employed as the film-forming plastic.

It has been found that best definition in the duplicated copy isproduced when the stencil-sheet assembly is arranged in direct contactor in close face to face relation with the heat-generating areas of thefilm. It has also been found that definition is improved when sufiicientheat is developed by the absorbed radiations in the minimum amount oftime. If prolonged exposure is used to develop adequate heat toaccomplish the desired changes in the stencil sheet, there is a tendencyfor this heat to flow sideways from the letter openings and consequentlyproduce excessively bold and ragged copy. In order to accomplish thedesired instantaneous but concentrated exposure, devices such as aphotographers flash lamp, as shown in Figure l, is preferred. Instead,use may be made of devices in which the source of infra-red ray-bearinglight is energized at high wattage by a capacitor similar to that whichis used in industrial spot-welding machines. Another device foraccomplishing the desired but short exposure to intense rays consists ofa relatively long but thin source of infra-red radiation such as a hotWire or tungsten filament lamp (as shown in Figure 4), the radiationfrom which is focused on the original through the use of suitable lensesand reflectors and which may be adapted to traverse the original atconstant speed so that the exposure of each line element is ofsubstantially equal intensity throughout. A still further device foraccomplishing the desired short but intense exposure consists of a pointsource of infra-red ray radiation, such as an incan descent lamp inwhich the radiation is focused to a relatively fine point through asystem of suitable lenses and reflectors onto the surface of the stencilsheet which is mounted with the master copy on a rapidly rotatingcylinder. During the rotation of the cylinder, the point source of lightmoves at constant speed in a direction parallel to the axis of thecylinder until each point element of the copy has been exposed to theconcentrated radiation.

It will be apparent from the description that a stencilsheet assemblyprepared in accordance with this invention will be capable of use forthe production of a large number of copies that correspond exactly withthe original. In view of the simplicity of the method of manufacture,coupled with the low cost of the materials involved, as well as thefailure to injure the original in any way during the manufacture of thestencil, the master can be discarded after use since one or more may beeasily prepared again from the original copy which may be filed away inusual ofiice practice. If desired, however, the stencil sheet may becleaned and preserved for subsequent use in the preparation ofadditional copies.

It will be apparent from the description that this invention provides abasically new method for preparing a stencil which conforms almostexactly with the copy. By the practice of directing the beams of lightonto predetermined and specified areas, it is possible by this method toprepare stencils for duplication of minor parts of a particular drawingor writing. To the best of my knowledge, this is the first time thatstencil duplication based upon a technique of this character has beenmade available for office copy work. It will be manifest that this sametechnique employing the phenomenon of heat generation from radiantenergy absorbed by the copy and reaction with an unsupported plasticfilm may be used for other duplicating processes, such for example as inthe production of hectograph masters or lithographic masters.

Although description has been limited to the use of an unsupported filmof ink impervious material for the manufacture of the new and improvedstencil, it will be understood that a physical support may be suppliedwith the film for the purpose of giving it greater strength forresisting the forces incident to normal handling and use and impartingmore desirable characteristics for handling and packaging. Such supportmay be provided in the form of an interlayer sheet or screen or it maybe a screen-like web or fabric substantially attached to or embedded inthe plastic material.

The technique herein described suggests itself for many other uses andfor many other variations, and it will be further understood thatnumerous changes may be made in the details of construction,arrangement, and operation, without departing from the spirit of theinvention, especially as defined in the following claims.

I claim:

1. In the method of producing a duplicating master from copy, the stepsof positioning the copy in surface contact with a thin ink imperviousunsupported, continuous film under stress of a film formingthermo-plastic resinous material, directing radiations rich in infra redupon the copy at an intensity and for a time to generate heat uponabsorption sufiicient when transferred to the thermo-plastic film tocause corresponding areas to be reduced to flowable condition forlateral displacement to form a plurality of interconnected openings inthe corresponding areas through which ink may pass.

2. In the method of producing a stencil from copy, the steps ofpositioning the copy substantially in surface contact with a continuous,unsupported thin ink impervious film under stress of a film formingplastic material reducible to flowable condition at elevatedtemperature, directing radiations rich in infra red upon the copy at anintensity and for a time to generate heat upon absorption sufficientwhen transferred to the plastic film to cause corresponding areas to bereduced to flowable condition for lateral displacement to form aplurality of interconnected openings in the corresponding areas throughwhich ink may pass.

3. In the method of producing a stencil from copy, the steps ofpositioning the copy substantially in surface contact with an oriented,ink impervious film of a film forming thermo-plastic material, directingradiations rich in infra red upon the copy at an intensity and for atime to generate heat upon absorption sufiicient when transferred to thethermo-plastic film to cause corresponding areas to be reduced tofiowable condition whereby openings form in the film through which inkmay pass.

4. The method as claimed in claim 3 in which the plastic film is basedupon a halogen containing thermoplastic resinous polymer.

5. The method as claimed in claim 3 in which the intensity of rays andtime of radiation is maintained to provide a temperature of aboutISO-450 F. in less than a few seconds.

6. The method as claimed in claim 3 in which the copy is positioned onthe thermoplastic film with the side having the letter outlines to bereproduced as stencil openings in face to face relation with the plasticfilm.

7. The method as claimed in claim 3 in which the copy is positioned on athermo-plastic film with the side having the letter outlines to bereproduced in the plastic film positioned away from the plastic film.

8. In the method of producing a stencil from copy, the steps ofpositioning the copy substantially in surface contact with a highlyoriented film of thermo-plastic material characterized by heatsensitivity which causes rearrangement of heated portions of the filminto a lattice work of resinous concentrations and openings therebetweenthrough which ink may pass, directing radiations rich in infra red at anintensity and for a time sufficient to generate heat which whentransferred to corresponding areas of the plastic film causerearrangement to form openings through which ink may pass.

9. In the method of producing a stencil directly from a copy, the stepof positioning the copy substantially in surface contact with anoriented ink impervious film of a resinous material selected from thegroup consisting of polyvinylidine chloride, polyvinyl chloride, vinylchloride-vinyl acetate copolymer, chlorinated rubber and rubberhydrochloride, directing radiations rich in infra red onto the copy atan intensity and for a time to generate a heat pattern corresponding tothat of the infra red absorbing-heat generating material in the copysulficient when transferred to the resinous film to cause cor respondingareas to be reduced to flowable condition whereby openings form in thefilm in corresponding areas through which ink may pass.

Murray Apr. 11,

